Kilojoule to Electronvolt Converter
Convert kilojoules to electronvolts with our free online energy converter.
Quick Answer
1 Kilojoule = 6.241509e+21 electronvolts
Formula: Kilojoule × conversion factor = Electronvolt
Use the calculator below for instant, accurate conversions.
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Kilojoule to Electronvolt Calculator
How to Use the Kilojoule to Electronvolt Calculator:
- Enter the value you want to convert in the 'From' field (Kilojoule).
- The converted value in Electronvolt will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Energy category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Kilojoule to Electronvolt: Step-by-Step Guide
Converting Kilojoule to Electronvolt involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
eV = kJ × 6.24151e+21Example Calculation:
1 kJ = 6.241509e+21 eV
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
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View all Energy conversions →What is a Kilojoule and a Electronvolt?
and Standards
The kilojoule is defined as exactly 1,000 joules:
1 kJ = 1,000 J = 1,000 kg·m²/s² = 1,000 N·m
Precise Equivalents
- 1 kJ = 1,000 J (exactly, by definition)
- 1 kJ = 0.239006 kilocalories (kcal, food Calories)
- 1 kJ = 0.947817 British thermal units (BTU)
- 1 kJ = 0.000277778 kilowatt-hours (kWh)
- 1 kJ = 6.242 × 10²¹ electronvolts (eV)
- 1 kcal = 4.184 kJ (exactly, thermochemical definition)
SI System Integration
The kilojoule is a standard SI unit formed by applying the metric prefix kilo- (1,000) to the base unit joule. Unlike the calorie, which has multiple definitions and creates confusion between small calories (cal) and large Calories (kcal), the kilojoule provides unambiguous measurement consistent across all scientific disciplines.
Nutrition Labeling Standards
International practice:
- Australia, New Zealand: kJ only (mandatory since 1995/2003)
- European Union: Both kJ and kcal required (kJ first, since 2016)
- China, Japan, South Korea: Primarily kJ with optional kcal
- Canada: Both kJ and kcal required
- United States: kcal only (Calories)
Standard format: "Energy: 250 kJ (60 Cal)" or "Energy: 1,000 kJ / 239 kcal"
The electronvolt (symbol: eV) is a unit of energy defined as the amount of kinetic energy gained (or lost) by a single electron when it moves through an electric potential difference of exactly one volt in vacuum.
Fundamental Definition
Mathematical Expression:
1 eV = e × 1 V
Where:
- e = elementary charge = 1.602176634 × 10⁻¹⁹ coulombs (exact, since 2019 SI redefinition)
- V = volt (SI unit of electric potential)
Since 1 volt = 1 joule per coulomb (J/C), we have:
1 eV = (1.602176634 × 10⁻¹⁹ C) × (1 J/C) = 1.602176634 × 10⁻¹⁹ J
This value is now exact by definition following the 2019 SI redefinition.
Physical Interpretation
Imagine a single electron starting at rest:
- Place electron at negative terminal of a 1-volt battery
- Let electron accelerate to the positive terminal through the electric field
- Kinetic energy gained by the electron = 1 electronvolt
The electron's final velocity would be approximately 593 km/s (ignoring relativistic effects), with kinetic energy:
KE = ½mv² = 1 eV = 1.602 × 10⁻¹⁹ J
Common Prefixes and Multiples
Standard SI Prefixes:
- meV (millielectronvolt) = 10⁻³ eV = 1.602 × 10⁻²² J (thermal energies, superconducting gaps)
- eV (electronvolt) = 1.602 × 10⁻¹⁹ J (atomic physics, visible light)
- keV (kiloelectronvolt) = 10³ eV = 1.602 × 10⁻¹⁶ J (X-rays, inner electrons)
- MeV (megaelectronvolt) = 10⁶ eV = 1.602 × 10⁻¹³ J (nuclear physics, gamma rays)
- GeV (gigaelectronvolt) = 10⁹ eV = 1.602 × 10⁻¹⁰ J (particle accelerators, rest masses)
- TeV (teraelectronvolt) = 10¹² eV = 1.602 × 10⁻⁷ J (LHC, highest-energy physics)
- PeV (petaelectronvolt) = 10¹⁵ eV = 0.1602 J (cosmic rays, ultra-high-energy astrophysics)
Electronvolt as Unit of Mass (E=mc²)
Through Einstein's mass-energy equivalence E = mc², the electronvolt can express mass:
Mass Unit: eV/c² (electronvolt divided by speed of light squared)
Conversion:
1 eV/c² = 1.782661921 × 10⁻³⁶ kg
Examples:
- Electron mass: me = 510.9989 keV/c² = 9.109 × 10⁻³¹ kg
- Proton mass: mp = 938.2720 MeV/c² = 1.673 × 10⁻²⁷ kg
- Neutron mass: mn = 939.5654 MeV/c² = 1.675 × 10⁻²⁷ kg
- Higgs boson mass: mH ≈ 125 GeV/c² (discovered 2012, CERN LHC)
Particle physicists routinely express masses in MeV/c² or GeV/c², often abbreviated to just MeV or GeV when context is clear.
Note: The Kilojoule is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Electronvolt belongs to the imperial/US customary system.
History of the Kilojoule and Electronvolt
and Evolution
The Joule Foundation: Mechanical Equivalent of Heat (1840s-1850s)
The kilojoule's origins trace to James Prescott Joule's groundbreaking experiments establishing that mechanical work and heat are equivalent forms of energy. His famous paddle-wheel experiments (1843-1850) demonstrated that a specific amount of mechanical work always produces the same amount of heat, establishing the mechanical equivalent of heat: approximately 4.184 joules per calorie.
This work unified thermodynamics and mechanics, providing the foundation for energy measurement in consistent units rather than the historically separate "calories" for heat and "work" for mechanical energy.
SI Adoption and the Joule as Standard (1960)
The International System of Units (SI) adopted the joule as the standard unit of energy in 1960, derived from the base units kilogram, meter, and second. The kilojoule naturally followed as the convenient multiple for everyday energy measurements, particularly for food and human metabolism where joule values would be inconveniently large (a typical meal contains millions of joules but only thousands of kilojoules).
International Nutrition Standards: WHO and FAO (1970s-1980s)
The World Health Organization (WHO) and Food and Agriculture Organization (FAO) began recommending kilojoules for international nutrition standards in the 1970s-1980s. Reports on dietary energy requirements transitioned from kilocalories to kilojoules to align with scientific practice and eliminate confusion between calories and Calories.
Key milestone: The 1985 FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements recommended expressing all energy values in both kilojoules and kilocalories, with kilojoules as the primary unit.
Australia: First Mandatory kJ Labeling (1995)
Australia became the first country to mandate exclusive kilojoule labeling on packaged foods in 1995, eliminating Calories entirely from nutrition panels. This bold move aimed to:
- Align consumer nutrition information with scientific standards
- Eliminate calorie/Calorie confusion
- Educate the public in metric energy units
- Standardize with international scientific practice
Reaction: Initial consumer confusion gave way to acceptance within 5-10 years. By 2005, surveys showed most Australians understood kilojoule values and could estimate daily requirements in kJ.
Menu labeling: In 2011, Australia extended kilojoule labeling to chain restaurant menus, requiring displayed kJ values for all items (but not Calories).
New Zealand and EU Adoption (2000s-2010s)
New Zealand followed Australia with mandatory kilojoule-only labeling in 2003.
The European Union required both kilojoules and kilocalories on nutrition labels from 2016 (under Regulation EU 1169/2011), with kilojoules listed first to emphasize the SI unit while maintaining familiarity for consumers accustomed to Calories.
United States: The Calorie Holdout
The United States remains the primary developed nation using kilocalories (Calories) exclusively on nutrition labels. The FDA updated nutrition fact panels in 2016 and 2020 without adopting kilojoules, citing consumer familiarity and the impracticality of changing established practice.
Scientific paradox: US nutrition scientists, exercise physiologists, and researchers routinely use kilojoules in academic publications while consumers encounter only Calories on products.
Global Status (2025)
Countries using kJ exclusively: Australia, New Zealand, Singapore (primary)
Countries using both kJ and kcal: European Union, Canada, China, Japan, South Korea, India, Brazil, Argentina, South Africa
Countries using kcal exclusively: United States, Myanmar
Population coverage: Over 85% of the world's population lives in countries where kilojoules appear on nutrition labels, either exclusively or alongside kilocalories.
The electronvolt's development parallels the history of atomic and nuclear physics in the early 20th century.
Pre-History: Early Electron Research (1897-1920s)
1897: J.J. Thomson discovers the electron using cathode ray tubes, observing electrons accelerated through electric potentials of hundreds of volts.
1909-1913: Robert Millikan's oil drop experiment precisely measures the elementary charge: e ≈ 1.6 × 10⁻¹⁹ C.
1913: Niels Bohr's model of the hydrogen atom calculates ionization energy as 13.6 eV (though he expressed it in ergs or joules).
1920s: Early atomic spectroscopy and quantum mechanics developments naturally worked with energies on the eV scale, though researchers still used CGS units (ergs) or SI joules.
Formalization (1930s-1940s)
Early 1930s: The term "electronvolt" begins appearing in physics literature as particle accelerators (cyclotrons, Van de Graaff generators) accelerate particles through kilovolt and megavolt potentials.
Key Motivation:
- Expressing X-ray energies: 10-100 keV far more intuitive than 10⁻¹⁵ to 10⁻¹⁴ J
- Nuclear reaction energies: Alpha particles with 5 MeV vs. 8 × 10⁻¹³ J
- Particle accelerator beam energies: 1 MeV proton beam vs. 1.6 × 10⁻¹³ J
1932: Carl Anderson discovers the positron (antimatter electron) in cosmic rays, with energies described in MeV.
1930s-1940s: Manhattan Project and nuclear weapons research standardized MeV for nuclear fission and fusion energies.
Post-War Standardization (1950s-1960s)
1948: 9th CGPM (General Conference on Weights and Measures) defines the ampere, indirectly fixing the volt and thus the electronvolt's joule equivalent.
1950s-1960s: Particle physics accelerators (synchrotrons, bevatrons) reach GeV energies:
- Brookhaven Cosmotron (1952): 3 GeV
- Berkeley Bevatron (1954): 6 GeV (first antiproton production)
- CERN Proton Synchrotron (1959): 28 GeV
Standard Practice: By the 1960s, eV/keV/MeV/GeV were universally adopted in atomic, nuclear, and particle physics.
Modern Era (1970s-Present)
1970s-1980s: TeV-scale energies anticipated and achieved:
- Fermilab Tevatron (1983): 1.96 TeV proton-antiproton collisions
2008-Present: CERN Large Hadron Collider (LHC):
- Design energy: 14 TeV (7 TeV per beam)
- Higgs boson discovery (2012): 125 GeV/c² mass
- Current: 13.6 TeV collision energy (2022-2025 Run 3)
2019 SI Redefinition:
- Elementary charge e defined exactly: 1.602176634 × 10⁻¹⁹ C
- Makes 1 eV = 1.602176634 × 10⁻¹⁹ J exact by definition
- Electronvolt recognized in SI Brochure as accepted non-SI unit
Beyond Accelerators:
- Semiconductor physics: Band gaps measured in eV (Si: 1.1 eV, GaN: 3.4 eV)
- Photovoltaics: Solar cell efficiency tied to band gap energies (1.1-1.7 eV optimal)
- Astronomy: Cosmic ray energies up to 10²⁰ eV (Oh-My-God particle, 1991)
Common Uses and Applications: kilojoules vs electronvolts
Explore the typical applications for both Kilojoule (imperial/US) and Electronvolt (imperial/US) to understand their common contexts.
Common Uses for kilojoules
1. Nutrition Labeling and Dietary Planning
The kilojoule is the international standard for expressing food energy content on nutrition labels, enabling consumers to track energy intake and manage weight.
Typical nutrition panel (Australia/NZ):
Nutrition Information
Servings per package: 5
Serving size: 30g
Per Serving Per 100g
Energy 600 kJ 2,000 kJ
Protein 3.0 g 10.0 g
Fat, total 5.0 g 16.7 g
- saturated 2.5 g 8.3 g
Carbohydrate 20.0 g 66.7 g
- sugars 5.0 g 16.7 g
Sodium 150 mg 500 mg
Weight management: To lose 0.5 kg per week, create a deficit of ~2,000 kJ (500 kcal) per day through reduced intake and increased activity.
2. Exercise Physiology and Sports Nutrition
Exercise scientists use kilojoules to quantify energy expenditure during physical activity and calculate fuel requirements for athletes.
Metabolic equivalent tasks (METs):
- 1 MET = resting metabolic rate ≈ 4.2 kJ per kg body weight per hour
- Moderate exercise = 3-6 METs = 12.6-25.2 kJ/kg/hr
- Vigorous exercise = 6+ METs = 25.2+ kJ/kg/hr
Example: A 70 kg person running at 8 METs for 1 hour:
- Energy = 70 kg × 8 METs × 4.2 kJ/kg/hr = 2,352 kJ (562 kcal)
3. Chemistry: Reaction Enthalpies
Chemists use kilojoules to express heat of reaction (ΔH), combustion energies, and bond energies.
Examples:
- Combustion of methane: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH = -890 kJ/mol
- Photosynthesis: 6CO₂ + 6H₂O + 2,870 kJ → C₆H₁₂O₆ + 6O₂
- Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 2,870 kJ
Bond energies (typical values in kJ/mol):
- C-H: 413 kJ/mol
- C-C: 348 kJ/mol
- C=C: 614 kJ/mol
- C≡C: 839 kJ/mol
- O-H: 463 kJ/mol
- N-H: 391 kJ/mol
4. Thermodynamics and Heat Transfer
Engineers use kilojoules for heat transfer calculations, thermal energy storage, and efficiency analysis.
Specific heat capacity (energy to raise 1 kg by 1°C):
- Water: 4.18 kJ/(kg·°C)
- Air: 1.01 kJ/(kg·°C)
- Aluminum: 0.90 kJ/(kg·°C)
- Concrete: 0.88 kJ/(kg·°C)
Example: Heating 50 liters (50 kg) of water from 20°C to 60°C:
- Energy = 50 kg × 4.18 kJ/(kg·°C) × (60-20)°C = 8,360 kJ (2.32 kWh)
5. Climate and Environmental Science
Climate scientists use kilojoules to quantify solar radiation, atmospheric energy budgets, and heat storage in oceans.
Solar irradiance: ~1,000 watts per square meter at Earth's surface = 3,600 kJ/m²/hr
Ocean heat content: Oceans store vast energy measured in zettajoules (10²¹ J), but marine biology and oceanography often express smaller values in kJ (e.g., energy available to marine organisms).
6. Consumer Energy Awareness
Kilojoule labeling on restaurant menus (mandatory in Australia, parts of US) helps consumers make informed choices.
Example chain restaurant menu (with kJ):
- Grilled chicken salad: 1,500 kJ
- Cheeseburger with fries: 4,200 kJ
- Vegetarian wrap: 1,800 kJ
- Large soft drink: 800 kJ
Daily context: If your target is 8,400 kJ/day, the cheeseburger meal consumes exactly half your daily budget.
When to Use electronvolts
Atomic and Molecular Physics
Scientists use eV to describe:
- Ionization energies: Energy required to remove electrons from atoms
- Electron affinity: Energy released when electron attaches to atom
- Molecular orbital energies: HOMO-LUMO gaps, band structures
- Spectroscopy: Photon energies in UV-vis spectroscopy (200-800 nm ≈ 6-1.5 eV)
Example: UV photoelectron spectroscopy (UPS) measures electron binding energies from 0-50 eV.
Nuclear and Particle Physics
The electronvolt (especially MeV, GeV, TeV) is the universal energy unit:
Particle Accelerators:
- Beam energies: "The LHC collides protons at 6.8 TeV per beam"
- Collision center-of-mass energy: √s = 13.6 TeV
Nuclear Reactions:
- Q-values: Energy released/absorbed (e.g., D-T fusion Q = 17.6 MeV)
- Decay energies: Alpha, beta, gamma emissions
Particle Properties:
- Rest masses: Particle Data Group lists masses in MeV/c² or GeV/c²
- Decay channels: Energy distributions of decay products
Semiconductor Device Physics
Band gap energies determine electronic and optical properties:
Applications:
- Solar cells: Optimal band gap ~1.3-1.5 eV for maximum efficiency under solar spectrum
- LEDs: Emission color determined by band gap (red ~1.8 eV, blue ~3.1 eV)
- Transistors: Threshold voltages and switching energies
- Detectors: Ionization energies for particle detection (Si: 3.6 eV per electron-hole pair)
Radiation Dosimetry and Medical Physics
X-ray and gamma-ray energies specified in keV or MeV:
Medical Imaging:
- Mammography: 25-35 keV (soft tissue contrast)
- CT scans: 80-140 keV
- PET scans: 511 keV (positron-electron annihilation photons)
Radiation Therapy:
- External beam: 6-18 MeV photon beams
- Proton therapy: 70-250 MeV proton beams
Astrophysics and Cosmology
Photon energies across the electromagnetic spectrum:
Radio to Infrared: μeV to eV (microwave background ~0.0002 eV) Visible: 1.8-3.1 eV X-ray: keV to MeV (neutron star accretion, supernovae) Gamma-ray: MeV to GeV (active galactic nuclei, gamma-ray bursts) Ultra-high-energy cosmic rays: EeV (10¹⁸ eV) and beyond
Example: Fermi Gamma-ray Space Telescope detects photons from 20 MeV to >300 GeV.
Materials Science and Catalysis
Surface science and chemical reactions:
Techniques:
- XPS (X-ray Photoelectron Spectroscopy): Binding energies 0-1500 eV
- UPS (UV Photoelectron Spectroscopy): Valence band energies 0-50 eV
- Auger Electron Spectroscopy: Electron energies 50-2000 eV
Catalysis:
- Activation barriers: 0.1-3 eV for chemical reactions
- Adsorption energies: 0.5-5 eV for molecules on surfaces
Additional Unit Information
About Kilojoule (kJ)
How do I convert kilojoules to Calories?
Formula: Calories (kcal) = kJ ÷ 4.184
Quick approximation: Divide kJ by 4 (slightly underestimates)
Examples:
- 100 kJ ≈ 24 Cal
- 500 kJ ≈ 120 Cal
- 1,000 kJ ≈ 239 Cal
- 2,000 kJ ≈ 478 Cal
- 8,400 kJ ≈ 2,007 Cal (daily intake)
Exact vs. approximate:
- 1,000 kJ ÷ 4 = 250 Cal (approximate, 4.6% high)
- 1,000 kJ ÷ 4.184 = 239 Cal (exact)
For dietary purposes, the approximate conversion (÷4) is usually sufficient.
How many kilojoules should I eat per day?
Daily kilojoule requirements depend on age, sex, body size, and activity level:
Adult women:
- Sedentary: 7,500-8,400 kJ/day (1,800-2,000 Cal)
- Moderately active: 8,400-9,600 kJ/day (2,000-2,300 Cal)
- Very active: 10,000-12,000 kJ/day (2,400-2,900 Cal)
Adult men:
- Sedentary: 8,800-10,000 kJ/day (2,100-2,400 Cal)
- Moderately active: 10,500-12,000 kJ/day (2,500-2,900 Cal)
- Very active: 12,500-14,500 kJ/day (3,000-3,500 Cal)
Children and teens: 5,000-12,500 kJ/day depending on age and activity
Athletes: 12,500-21,000 kJ/day (3,000-5,000 Cal) or more during intense training
General guideline: Most adults need 8,000-10,000 kJ daily (~2,000-2,400 Cal).
Why do some countries use kJ instead of Calories?
Scientific consistency: Kilojoules are SI units, consistent with all other scientific measurements (meters, kilograms, seconds). Calories are non-SI legacy units.
Eliminates confusion: The calorie system is inherently confusing:
- Small calorie (cal) = 4.184 J
- Large Calorie (kcal, "food Calorie") = 1,000 cal = 4,184 J
- Many people don't realize "Calories" on food labels are actually kilocalories
Kilojoules eliminate this ambiguity—1 kJ always equals 1,000 J.
International standardization: The WHO, FAO, and international scientific community use kilojoules as the standard for nutrition research and policy.
Countries using kJ:
- Exclusive kJ: Australia, New Zealand, Singapore
- Both kJ and kcal: EU (27 countries), Canada, China, Japan, India, Brazil, Argentina, South Africa
- Only kcal: United States (and a few small nations)
Result: Over 85% of the world's population sees kilojoules on food labels.
How many kilojoules do I burn exercising?
Energy expenditure varies by activity intensity, body weight, fitness level, and efficiency:
General estimates (per hour for 70 kg person):
- Walking (5 km/h): 1,200-1,500 kJ (290-360 Cal)
- Jogging (8 km/h): 2,500-3,000 kJ (600-720 Cal)
- Running (12 km/h): 3,500-4,200 kJ (840-1,000 Cal)
- Cycling (leisure): 1,200-1,600 kJ (290-380 Cal)
- Cycling (vigorous): 2,500-3,300 kJ (600-800 Cal)
- Swimming (moderate): 2,000-2,500 kJ (480-600 Cal)
- Weight training: 1,200-2,100 kJ (290-500 Cal)
- Yoga: 650-1,000 kJ (155-240 Cal)
Per-distance estimates:
- Walking: 200-250 kJ/km (50-60 Cal/km)
- Running: 300-350 kJ/km (70-85 Cal/km)
- Cycling: 100-150 kJ/km (25-35 Cal/km)
Formula (approximate): kJ/hr ≈ Body weight (kg) × MET value × 4.2
Where MET = metabolic equivalent (1 MET = resting, 3-6 = moderate, 6+ = vigorous)
Are kilojoules more accurate than Calories for nutrition?
Same accuracy, different units: Both kJ and kcal measure the same physical quantity (energy) with equal precision. The accuracy of nutrition labeling depends on measurement methods (bomb calorimetry, Atwater system), not the choice of units.
Advantages of kilojoules:
- SI consistency: Compatible with all other scientific units
- No ambiguity: 1 kJ always means 1,000 J (unlike calorie/Calorie confusion)
- International standard: Used in scientific literature worldwide
- Educational: Connects food energy to physics and chemistry
Advantages of Calories (kcal):
- Familiarity: Deeply established in US consumer culture
- Smaller numbers: 2,000 Cal/day sounds less intimidating than 8,400 kJ/day
- Historical data: Decades of dietary research in kcal
Scientific community consensus: Kilojoules are preferred for publications, while kcal persists in US consumer contexts due to inertia.
Can I lose weight by tracking kilojoules?
Yes—identical to tracking Calories: Weight loss requires a sustained energy deficit (consuming fewer kJ than you expend). Whether you count in kJ or kcal makes no difference physiologically.
Creating a deficit:
- 0.5 kg/week loss: Deficit of ~2,000 kJ/day (500 kcal/day)
- 1 kg/week loss: Deficit of ~4,000 kJ/day (1,000 kcal/day)
Practical approach:
- Calculate maintenance: Estimate daily kJ needs (8,000-12,000 kJ for most adults)
- Set deficit: Reduce intake by 1,500-2,500 kJ/day (moderate, sustainable)
- Track intake: Log food kJ using labels or apps
- Monitor progress: Adjust based on weekly weigh-ins
Example: If you need 10,000 kJ/day to maintain weight, eating 8,000 kJ/day creates a 2,000 kJ deficit = ~0.5 kg loss per week.
How accurate are kilojoule values on food labels?
Regulatory tolerances allow some variation:
Australia/NZ: ±20% tolerance for energy values (same as nutrients)
EU: Energy values must be calculated using standard conversion factors (Atwater system) or measured via bomb calorimetry. Tolerances apply.
Sources of inaccuracy:
- Natural variation: Agricultural products vary in composition
- Rounding: Labels round to nearest 10-100 kJ
- Calculation methods: Atwater factors (17 kJ/g carb, 38 kJ/g fat) are averages
- Serving size: Manufacturers sometimes understate serving sizes, making total kJ appear lower
Reality: Most packaged food kJ values are reasonably accurate (within ±10-15%), but restaurant/takeaway items may vary more significantly. Track trends over weeks rather than obsessing over individual items.
What is the relationship between kJ and metabolism?
Basal metabolic rate (BMR): The energy your body needs at rest to maintain vital functions (breathing, circulation, cell production) is typically:
- Women: 5,000-6,500 kJ/day (1,200-1,550 kcal/day)
- Men: 6,500-8,000 kJ/day (1,550-1,900 kcal/day)
Total daily energy expenditure (TDEE): BMR × activity factor
- Sedentary (little exercise): BMR × 1.2
- Lightly active (1-3 days/week): BMR × 1.375
- Moderately active (3-5 days/week): BMR × 1.55
- Very active (6-7 days/week): BMR × 1.725
- Extra active (twice daily, heavy): BMR × 1.9
Metabolic efficiency: Humans convert food energy to mechanical work at only ~25% efficiency. The other ~75% becomes heat. This is why intense exercise makes you hot!
Example: Running requires ~300 kJ/km of mechanical work, but your body actually burns ~1,200 kJ/km of food energy to produce that work (300 kJ useful, 900 kJ heat).
How do kilojoules relate to weight gain or loss?
Energy balance equation:
- Weight maintenance: Energy in (kJ consumed) = Energy out (kJ expended)
- Weight gain: Energy in > Energy out → Surplus stored as fat/muscle
- Weight loss: Energy in < Energy out → Deficit drawn from body stores
Fat energy density: 1 kg body fat ≈ 0.87 kg pure fat ≈ 33,000 kJ (7,700 kcal)
Weight loss calculation:
- To lose 0.5 kg/week: Create 4,700 kJ weekly deficit = 670 kJ/day deficit
- To lose 1 kg/week: Create 9,400 kJ weekly deficit = 1,340 kJ/day deficit
Practical example:
- Maintenance: 10,000 kJ/day
- Target: Lose 0.5 kg/week
- Daily intake: 10,000 - 670 = 9,330 kJ/day (2,230 kcal/day)
- Or: Eat 10,000 kJ but burn extra 670 kJ through exercise
Sustainable approach: Combine moderate deficit (1,500-2,000 kJ/day) with regular activity for gradual, maintainable weight loss.
Is 8,400 kJ per day a standard recommendation?
8,400 kJ (~2,000 kcal) is a common reference value for nutrition labeling (e.g., "% daily value" on labels), representing an average adult's needs. However:
Not universal: Individual needs vary by:
- Age: Older adults typically need less
- Sex: Men generally need more than women
- Body size: Larger bodies need more energy
- Activity level: Active people need significantly more
- Metabolism: Varies 10-20% between individuals
Who needs ~8,400 kJ/day?
- Sedentary to moderately active women
- Sedentary men
- Older adults
Who needs more?
- Active/very active men (10,000-14,000 kJ/day)
- Athletes (12,500-21,000+ kJ/day)
- Teenagers (especially boys)
Who needs less?
- Children (5,000-7,500 kJ/day depending on age)
- Very sedentary older adults (7,000-7,500 kJ/day)
Recommendation: Use 8,400 kJ as a starting point, then adjust based on whether you're maintaining, losing, or gaining weight.
About Electronvolt (eV)
How do I convert eV to joules?
Formula: Joules = eV × 1.602176634 × 10⁻¹⁹
Example: 5 eV to joules
- 5 × 1.602 × 10⁻¹⁹ = 8.01 × 10⁻¹⁹ J
Reverse (joules to eV): eV = J / (1.602 × 10⁻¹⁹)
What is an electronvolt in simple terms?
An electronvolt is the tiny amount of energy that one electron gains when it "falls" through an electric potential difference of one volt, similar to a ball rolling down a one-meter hill gaining gravitational potential energy.
Analogy: Imagine a tiny charged particle (electron) on a "voltage hill." Rolling it down a 1-volt slope gives it 1 eV of energy.
Why use electronvolts instead of joules?
Convenience: Atomic and subatomic energies are incredibly small in joules, making eV more practical:
- Hydrogen ionization: 13.6 eV vs. 2.18 × 10⁻¹⁸ J
- LHC collision: 13 TeV vs. 2.1 × 10⁻⁶ J
- Higgs boson mass: 125 GeV/c² vs. 2.2 × 10⁻²⁵ kg
Natural scale: The electronvolt matches the energy scales in atomic/nuclear/particle physics, just as kilometers are more natural than microinches for geography.
How is energy related to wavelength in eV?
Formula: E (eV) ≈ 1240 / λ (nm)
Precise formula: E = hc/λ = (1239.84193 eV·nm) / λ (nm)
Where:
- h = Planck's constant = 4.136 × 10⁻¹⁵ eV·s
- c = speed of light = 3 × 10⁸ m/s
Examples:
- Red light (620 nm): E = 1240 / 620 = 2.0 eV
- Blue light (400 nm): E = 1240 / 400 = 3.1 eV
- X-ray (0.1 nm): E = 1240 / 0.1 = 12,400 eV = 12.4 keV
What is the difference between eV and eV/c²?
- eV = unit of energy
- eV/c² = unit of mass (through E=mc²)
Example:
- Photon energy: 2 eV (pure energy, massless particle)
- Electron rest mass: 511 keV/c² (intrinsic mass)
- When electron at rest, its rest energy E₀ = mc² = 511 keV
Why divide by c²? To convert from energy units (eV) to mass units, divide by c² = (3 × 10⁸ m/s)².
How many eV in visible light?
Visible spectrum: approximately 1.8 eV (red) to 3.1 eV (violet)
Detailed breakdown:
- Red (700 nm): 1.77 eV
- Orange (620 nm): 2.00 eV
- Yellow (580 nm): 2.14 eV
- Green (520 nm): 2.38 eV
- Blue (470 nm): 2.64 eV
- Violet (400 nm): 3.10 eV
Why this range? Human eye evolved to detect solar spectrum peak output (~500 nm, 2.5 eV).
What is a kiloelectronvolt (keV)?
1 keV = 1,000 eV = 1.602 × 10⁻¹⁶ J
Typical applications:
- X-ray energies: 10-100 keV (medical, industrial)
- Inner-shell electron binding energies: 0.1-100 keV
- Low-energy nuclear transitions: 1-1000 keV
- Electron microscope beam energies: 100-300 keV
What is the energy of thermal motion at room temperature?
Room temperature (T = 300 K): kBT ≈ 0.026 eV = 26 meV (millielectronvolts)
Where:
- kB = Boltzmann constant = 8.617 × 10⁻⁵ eV/K
- T = absolute temperature in kelvins
Significance:
- Explains why chemical bonds (1-10 eV) don't spontaneously break at room temperature
- Thermal energy << bond energy, so molecular stability maintained
- Important for semiconductor physics: band gap >> kBT for good insulator
How much energy is in a MeV?
1 MeV (megaelectronvolt) = 1,000,000 eV = 1.602 × 10⁻¹³ J
Typical MeV-scale phenomena:
- Nuclear binding energies: ~8 MeV per nucleon
- Gamma rays: 0.1-10 MeV
- Positron-electron annihilation: 2 × 0.511 = 1.022 MeV (two 511 keV photons)
- Alpha particle decay energies: 4-9 MeV
- Nuclear fission fragments: 50-200 MeV
What is the Higgs boson mass in eV?
Higgs boson mass: mH ≈ 125.1 GeV/c²
Discovered at CERN's Large Hadron Collider (LHC) on July 4, 2012.
Context:
- About 133 times heavier than a proton (938 MeV/c²)
- Equivalent to approximately 133 hydrogen atoms in mass
- In kilograms: 2.24 × 10⁻²⁵ kg (incredibly tiny, but "heavy" for elementary particles)
The Higgs boson's mass is crucial to understanding the Higgs mechanism, which gives fundamental particles their mass through interaction with the Higgs field.
Can you use eV for macroscopic energies?
Technically yes, but impractical:
Examples:
- 1 joule = 6.242 × 10¹⁸ eV (6 billion billion eV!)
- 1 kilowatt-hour (kWh) = 3.6 × 10⁶ J = 2.25 × 10²⁵ eV
- AA battery (3 Wh) = 6.75 × 10²² eV
Why not used: Numbers become absurdly large. The electronvolt is designed for atomic/molecular/nuclear scales, not everyday human-scale energies.
Exception: Ultra-high-energy cosmic rays occasionally reach macroscopic energies:
- Oh-My-God particle (1991): 3 × 10²⁰ eV ≈ 51 joules (energy of baseball at 100 km/h)
Conversion Table: Kilojoule to Electronvolt
| Kilojoule (kJ) | Electronvolt (eV) |
|---|---|
| 0.5 | 3,120,754,537,230,381,400,000 |
| 1 | 6,241,509,074,460,763,000,000 |
| 1.5 | 9,362,263,611,691,144,000,000 |
| 2 | 12,483,018,148,921,525,000,000 |
| 5 | 31,207,545,372,303,810,000,000 |
| 10 | 62,415,090,744,607,620,000,000 |
| 25 | 156,037,726,861,519,070,000,000 |
| 50 | 312,075,453,723,038,140,000,000 |
| 100 | 624,150,907,446,076,300,000,000 |
| 250 | 1,560,377,268,615,190,700,000,000 |
| 500 | 3,120,754,537,230,381,400,000,000 |
| 1,000 | 6,241,509,074,460,763,000,000,000 |
People Also Ask
How do I convert Kilojoule to Electronvolt?
To convert Kilojoule to Electronvolt, enter the value in Kilojoule in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our energy converter page to convert between other units in this category.
Learn more →What is the conversion factor from Kilojoule to Electronvolt?
The conversion factor depends on the specific relationship between Kilojoule and Electronvolt. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Electronvolt back to Kilojoule?
Yes! You can easily convert Electronvolt back to Kilojoule by using the swap button (⇌) in the calculator above, or by visiting our Electronvolt to Kilojoule converter page. You can also explore other energy conversions on our category page.
Learn more →What are common uses for Kilojoule and Electronvolt?
Kilojoule and Electronvolt are both standard units used in energy measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our energy converter for more conversion options.
For more energy conversion questions, visit our FAQ page or explore our conversion guides.
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Explore other energy units and their conversion options:
- Joule (J) • Kilojoule to Joule
- Megajoule (MJ) • Kilojoule to Megajoule
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- Kilowatt-hour (kWh) • Kilojoule to Kilowatt-hour
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- Therm (therm) • Kilojoule to Therm
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Fundamental physical constants and unit conversions
Bureau International des Poids et Mesures — International System of Units (SI) definitions and standards
International Organization for Standardization — Quantities and units international standards series
Last verified: February 19, 2026